Medical catheters are used for innumerable minimally invasive medical procedures. Catheters may be used, for example, for delivery of therapeutic drug doses to target tissue and/or for delivery of medical devices such as lumen-reinforcing or drug-eluting stents. Likewise, catheters may be used to guide medical instruments to a target site to perform a surgical procedure, such as tissue rescission, ablation of obstructive deposits or myocardial revascularization.
Currently, myocardial injection devices are used to deliver therapeutics, for example, cell and viral therapeutics, to the myocardial wall to stimulate myocardial angiogenesis and myocardial tissue regeneration. Unfortunately, not all patients have ventricular walls of equal thickness, which makes it difficult to treat those patients with thin ventricular walls with a needle having a single depth. For example, if the depth of injection of the needle causes the needle tip to extend through the ventricular wall, the therapeutic will not be delivered to the desired location, and thus the effectiveness of the procedure will be compromised. Similarly, there is a wide range of wall thicknesses even within a single patient's heart, which requires multiple needles, each with a different depth of injection. As a result, procedural times and costs are increased due to using and switching between multiple needles.
Compounding the difficulty of using the correct depth of injection is the loss/gain in needle length due to the bending and curving of the catheter to reach the desired tissue site. For example, when a catheter lumen is inserted into and moved through a body, a needle lumen that is disposed within the catheter lumen will be subjected to similar movements and bends. However, for a variety of reasons, for example, friction between the inner and outer lumens, the amount of space between the inner and outer lumens, and different levels of lumen flexibility, the distal end of the inner lumen may not remain in the same relative position to the distal end of the outer lumen when the catheter is in a curved position as when it is in a straight position. In the case where the inner lumen is not as flexible as the outer lumen and the outer lumen has been contorted to have numerous curves, the inner lumen may extend past the end of outer lumen because it has taken a “path of least resistance” to short-cut through the curves in the outer lumen. As a result, the tip of the needle may extend out of the distal end of the catheter, thus making it difficult to move the end of the catheter without damaging tissue. In addition, having the tip of the needle extend out of the distal end of the catheter may change the depth of the injection to be too deep. Conversely, if friction prevents the inner lumen from moving the same amount as the outer lumen, the tip of the needle may not extend to its normal position within the outer lumen at the distal end of the catheter, thus reducing the depth of or even preventing the injection all together. For example, if the depth of injection is to be 2 mm and the inner needle lumen has receded 1.5 mm from its at rest position near the distal end of the catheter, then the actual depth of the injection will only be 0.5 mm.